This invention relates to a resonator which is provided in a multilayer board including a power plane and a ground plane, and which is configured to reduce a noise, particularly a high frequency noise, generated between the power plane and the ground plane.
An electronic device such as a personal computer (PC) has a printed circuit board installed therewithin. In general, the installed printed circuit board is a multilayer board including a power plane, a ground plane and a signal plane. The thus-formed multilayer board generates various high frequency noises under some conditions.
Each of Patent Document 1 (JPA 2004-140210) and Nonpatent Document 1 (Hiroyasu Sano, Yoshiaki Maruyama and Akihiro Tokikawa, “A Study of the Optimal Selection of Parts to Reduce the Power Ground Plane Resonance”, Shingaku Gihou, The Institute of Electronics, Information and Communication Engineers, July 2012, volume 112, issue 130, pages 19 to 21) discloses a structure of the multilayer board for reducing the aforementioned noises, contents of Patent Document 1 and Nonpatent Document 1 are incorporated herein by reference.
A substrate (multilayer board) of Patent Document 1 comprises a power-supply voltage plane (power plane), a base voltage plane (ground plane), a signal wiring plane (signal plane) and a stub plane. The power-supply voltage plane is configured to supply electric power from a main power source through a power supplying path. The signal wiring plane has large scale integration (LSI) packages (electronic components) mounted thereon. The stub plane is provided with a stub. The power-supply voltage plane and the base voltage plane are connected with each other via a capacitor. The capacitor is provided between the power-supply voltage plane and the LSI packages in the power supplying path. The stub is provided between the main power source and the capacitor in the power supplying path. The stub has a connected end and an open end. The connected end extends through a dielectric layer to be connected to the base voltage plane or the power-supply voltage plane. According to the Patent Document 1, since the stub has a length which is equal to a quarter of a wavelength of a synchronous switching noise caused by the LSI packages, the synchronous switching noise (i.e. the noise due to the clock synchronization of the LSI packages) can be reduced.
Nonpatent Document 1 discloses a power plane and a ground plane connected with each other via one or more snubber circuits. Each of the snubber circuits consists of a capacitor and a resistor connected in series. According to Nonpatent Document 1, if the snubber circuit is adjusted to have proper characteristics such as a proper resistance, it is possible to reduce an undesirable radiation noise and to prevent a malfunction of an electric device which might be caused by resonance between the power plane and the ground plane.
In general, a power plane and a ground plane of a multilayer board are required to be provided with an insulator layer (i.e. a dielectric layer) therebetween. As disclosed in Nonpatent Document 1, a parallel plate resonance may be generated between the thus-arranged power plane and ground plane so that the electric device does not behave properly and the undesirable noise is radiated. Such noise that is caused from the multilayer board itself cannot be reduced by using the technology disclosed in Patent Document 1. Moreover, according to the technology disclosed in Nonpatent Document 1, the characteristics (for example, the resistance), of the snubber circuit cannot be properly designed until an arrangement of electric components on a signal plane is determined. In addition, a plurality of the snubber circuits is necessary to reduce the respective noises having various frequencies. However, it is difficult to properly adjust the resistance of each of the snubber circuits. Thus, the technology disclosed in Nonpatent Document 1 is not effective to reduce the parallel plate resonance generated between the power plane and the ground plane and, therefore, is not effective to prevent the malfunction of the electric device or to reduce the undesirable radiation noise caused by the parallel plate resonance.